Non-classical response of solid helium confined in Vycor glass*

The non-classical rotational inertia of solid $^{4}$He was observed by a series of torsional oscillator experiments[1]. Probable heat capacity signature of the supersolid transition which coincides with the non-classical mass decoupling is also observed[2]. Recent torsional oscillator experiments suggest that disorder and the orientation of a helium crystal may play an important role in the appearance of non-classical rotational inertia. Accordingly, the investigation on the role of defects and crystal orientation may provide crucial clues to understand supersolidity. Solid helium confined in porous media cannot possess well-defined crystal orientation and is likely heavily populated with defects. Here we will present the pressure dependence of the non-classical rotational inertia in solid helium confined in Vycor glass by torsional oscillator techniques. [1] E. Kim and M. H. W. Chan, \textit{Science} \textbf{305}, 1941 (2004); \textit{Nature} \textbf{425}, 227 (2004); \textit{J. Low Temp. Phys.} \textbf{138}, 859 (2005); \textit{Phys. Rev. Lett. }\textbf{97}, 115302 (2006). [2] X. Lin, A. C. Clark, M. H. W. Chan, \textit{Nature} \textbf{449,}1025(2007).